1. Field of the Invention
The present invention relates to the production of steel from solid iron containing metallic pieces such as scrap iron, solid pig iron, iron pellets, iron sponge and the like in a blown oxygen converter which is equipped with submerged injection jets for both oxygen and pulverized fuels containing carbon.
2. Description of the Prior Art
At the present time, the production of steel from scrap iron without the addition of liquid crude iron is preferably carried out in electric-arc furnaces. By the profitability of such a process depends largely upon the price of electric energy. The known converter procedures, wherein oxygen is blown onto or through the fused mass, work quicker and more efficiently, as far as cost is concerned, then the electric-arc furnaces. But in these latter processes, liquid crude iron is generally required for the production of steel in the converter, with scrap iron being added as a cooling medium, in relationship to its composition, in the refining process. Usually, the proportion of scrap iron in relation to the weight of steel amounts to approximately 30%.
More recently converter procedures have been proposed which make it possible to increase the proportion of scrap iron such that steel may be produced entirely from solid iron containing pieces such as scrap iron. To do this, the required heat is introduced by preheating and melting the scrap iron and then feeding fuels containing carbon into the fused mass. In such processes, the profitability is essentially determined by the pyrometric efficiency of the fuels that are used.
In the old German Pat. Nos. 508,966 and 537,781 of 1924 and 1929 respectively, a converter procedure for smelting ore is described wherein coal dust and oxygen, or oxygen-enriched air, are introduced into the fused mass. The introduction of such fuels and the conveying of the required heat to the fused mass obviously was difficult, for it was subsequently proposed, in supplementary German Pat. No. 537,781, that the procedure of German Pat. No. 508,966 should be conducted in an electrically heated converter.
German Pat. No. 28 38 983, entitled "Procedure for Delivering Heat in the Production of Steel in a Converter", describes a method of operation whereby the scrap iron charge to the converter may be increased at will to finally produce a fused mass of steel made entirely from solid iron containing pieces. According to the procedure of this publication, the converter is charged with scrap iron which is then preheated for approximately 10 minutes. During the preheating phase, oxygen injection jets located in the bottom of the converter work as burners. After the preheating step, liquid crude iron may be charged into the converter or the burners may continue to work without the addition of crude iron. As soon as the contents of the converter are completely melted to present a fused mass, a pulverized carbon containing fuel, such as coke or coke powder, and oxygen surrounded by a hydrocarbon containing protective medium are blown through submerged jets located beneath the surface of the molten mass. Approximately the same amount of oxygen as is introduced under the surface of the mass is blown simultaneously onto the upper surface of the mass through the open converter space.
In the practical application of the foregoing procedure, it has become evident that as the proportion of crude iron charged in relation to the final weight of steel produced is reduced until solid iron containing pieces are used exclusively, the smelting time is extended out of all proportion and the overall length of the time of the process is correspondingly increased. Furthermore, the consumption of energy is variable during this smelting phase, and increases a bit, on the average. Consequently, without using liquid crude iron this procedure cannot be carried out as reliably or as profitably as can be done when using a minimum quantity of a crude-iron fused mass. A lengthened time of operation can be expected and fluctuations in the pyrometric efficiency of the fuel being used will occur during the scrap iron smelting period.